The present invention relates to a differential pressure detecting equipment provided with a condenser having an inner condenser chamber used for a steam containing non-condensible gases, typically represented by, for example, a reactor water level measuring apparatus for measuring the reactor water level of a boiling water reactor.
As one typical example of a conventional differential pressure detecting equipment, there is provided a reactor water level measuring apparatus.
In a boiling water reactor as a light water reactor, a reactor pressure vessel is accommodated in a reactor containment vessel and the reactor water level of the reactor pressure vessel is usually measured by a reactor water level measuring apparatus making use of a pressure difference. A pressure difference type water level gauge is used in a conventional reactor water level measuring apparatus and a reactor water level measuring apparatus using the pressure difference type water level gauge will be described with reference to FIGS. 12 and 13.
A reactor pressure vessel 2 accommodated in a reactor containment vessel 1 is provided with a steam phase side pressure detector 4 located above a reactor water level WL above a core 3 and a liquid phase side pressure detector 5 located in a coolant (reactor water) below the water level WL, respectively.
The steam phase side pressure detector 4 of the reactor pressure vessel 2 is connected to a condenser 7, such as condenser tank, defining a condenser chamber, through an upwardly inclining connection pipe 6 and the condenser tank 7 cools and condenses the steam from the reactor pressure vessel 2 to water. A reference water column side instrument pipe 8 extends from the bottom of the condenser tank 7 and is connected to the high pressure side of a differential pressure detector 9. The pressure difference sensor 9 is installed externally of the reactor accommodating vessel 1.
A variable water column side instrument pipe 10 connected to the liquid phase side pressure detector 5 is connected to the low pressure side of the differential pressure detector 9 and a water head pressure resulting from the reactor water level WL acts on the differential pressure detector 9 through the instrument pipe 10. The water head pressure varies in accordance with the variation of the reactor water level WL.
Incidentally, the stream guided from the reactor pressure vessel 2 to the condenser tank 7 through the connecting pipe 6 is cooled and condensed in a condenser chamber 11 in the condenser tank 7 because the temperature of a condenser main body is lower than the temperature of saturated steam and stays in a liquid basin 11a formed on the bottom of the condenser tank 7 and in the reference water column side instrument pipe 8. Excessive water condensed in the condenser tank 7 returns to the reactor pressure vessel 2 as spill-over water because the connection pipe 6 inclines downward toward the reactor pressure vessel 2 so that a reference water level SWL is maintained in the condenser tank 7. A reference water head pressure resulting from the reference water level SWL acts on the high pressure side of the differential pressure detector 9.
As described above, since the reference water head pressure resulting from the reference water level SWL of the condenser tank 7 and a variable water head pressure resulting from the reactor water level WL are applied to the differential pressure detector 9, this detector 9 detects the difference between these water head pressures and outputs an electric signal converted in accordance with the pressure difference as a reactor water level signal S.
When the reactor water level WL is high, the variable water head pressure resulting from the water level WL increases and the pressure difference acting on the differential pressure detector 9 decreases, whereas when the reactor water level is low, the variable water head pressure resulting from the reactor water level WL decreases and the pressure difference acting on the differential pressure detector 9 increases.
As described above, the differential pressure detector type water level measuring apparatus using a condenser tank is utilized for various water level measuring apparatus in nuclear power plants, thermal power plants, chemical plants or the like, as well as flow meters therefor. When utilized for the flow meters, such flow meter is provided with, in substitution for the variable water column conduit in the water level measuring apparatus, a condenser tank and instrument pipes of the differential pressure detector type water level measuring apparatus of the type described above. However, the basic principle, that the water head difference of the instrument pipes is compared by the differential pressure detector and then a differential signal is outputted, is identical.
The conventional water level measuring apparatus of the boiling water reactor of the characteristics described above provides the following problems.
In the conventional reactor water level measuring apparatus, since the steam generated in the core 3 of the reactor pressure vessel 2 contains oxygen and hydrogen produced when the radioactive rays from a coolant (water) is decomposed in the core 3, there is a possibility that when the steam flowing from the steam phase side pressure detector 4 through the connection pipe 6 is condensed in the condenser tank 7, the oxygen and hydrogen as non-condensable gases are accumulated in a gas phase basin 11b located in the upper portion of the condenser tank 7.
As described above, there is a possibility that the accumulation of non-condensable gases in the condenser tank 7 is accelerated, the partial pressure of the non-condensable gases in the condenser tank 7 increases and an amount of dissolution of the non-condensable gases below the reference water level SWL and in the reference water column side instrument pipe 8 increases in the process in which the steam flowing from the reactor pressure vessel 2 is condensed in the condenser tank 7 depending upon the disposition and development of the connection pipe 6 interposed between the steam phase side pressure detector 4 and the condenser 7.
When the pressure in a reactor abruptly drops such as in loss of coolant accident (LOCA) in the state that oxygen and hydrogen are accumulated in the condenser tank 7, there is a possibility that the non-condensable gases dissolved below the reference water level SWL in the condenser tank 7 and in the water in the reference water column side instrument pipe 8 expand and push the water in the reference water column side instrument pipe 8 upward as well as the water staying in the condenser tank 7 and forming the reference water level SWL is pushed and returned into the reactor pressure vessel 2.
As a result, the reference water level SWL applying a certain reference water head pressure to the high pressure side of the differential pressure detector 9 abruptly varies and finally lowers. At the time, since the reference water level SWL lowers regardless of whether a pressure detected by the liquid phase side pressure detector 5 provided in the coolant of the reactor pressure vessel 2 is kept to a certain level, a pressure difference applied to the differential pressure detector 9 drops, thus causing a possibility that the reactor water level WL in the reactor pressure vessel 2 measures an apparent level which is higher than an actual level.
Since the above matters lead to an overestimation of an amount of water as a coolant held in the reactor, it has been desired for a reactor water level measuring apparatus to accurately measure a reactor water level from a view point of the improvement of operational reliability.